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Intermittent fasting (IF) is an umbrella term for various diets that cycle between a period of fasting and non-fasting during a defined period. Intermittent fasting can also be used with calorie restriction for weight loss.[1]

Contents

1 Practice and variations

2 Research

3 See also

4 References

Practice and variations[edit]

Some people may use intermittent fasting to diminish caloric intake and lose weight.[2][3] Preliminary research indicates that intermittent fasting may affect risk factors for some diseases.[3]

Whole-day fasting involves regular one-day fasts. The strictest form would be Alternate day fasting (ADF). This involves a 24-hour fast followed by a 24-hour non-fasting period.[4] The 5:2 diet allows the consumption of 500–600 calories on fasting days.[5][6]

Time-restricted feeding (TRF) involves eating only during a certain number of hours each day.[7] A common form of TRF involves fasting for 16 hours each day and only eating during the remaining 8 hours, typically on the same schedule each day.[8] A more liberal practice would be twelve hours of fasting and a twelve-hour eating window, or a stricter form would be to eat one meal per day, which would involve around 23 hours of fasting per day.[9]

Recommendations vary on what can be consumed during the fasting periods. Some would say only water, others would allow tea or coffee (without milk or sugar) or zero-calories drinks with artificial sweeteners. Yet others would allow “modified fasting” with limited caloric intake (e.g., 20% of normal) during fasted periods rather than none at all.[4]

The 5:2 diet became popular in the UK in 2012[10][11][12] after the BBC2 television Horizon documentary Eat, Fast and Live Longer.[13] Via sales of best-selling books, it became widely practiced.[6][14]

According to NHS Choices as of 2012, people considering the 5:2 diet should first consult a physician, as fasting can sometimes be unsafe.[6][15] In the UK, the tabloid press reported on research claiming the 5:2 diet could reduce the risk of breast cancer, improve brain and immune functions, or extend lifespan, but there is inadequate evidence for such statements.[6][16] A news item in the Canadian Medical Association Journal expressed concern that promotional material for the diet showed people eating high-calorie food such as hamburgers and chips, and that this could encourage binge eating since the implication was that “if you fast two days a week, you can devour as much junk as your gullet can swallow during the remaining five days”.[17]

Research[edit]

A 2014 review described that intermittent fasting has not been studied in children, the elderly, or the underweight, and could be harmful in these populations.[18] It also suggested that people choosing to fast for periods of time greater than 24 hours should be monitored by a physician, as changes to the gastrointestinal system or circadian rhythm can occur.[18] The review concluded that fasting is unlikely to have much effect on conditions other than obesity, such as aging or other chronic conditions, unless combined with long-term calorie restriction and a plant-based diet, such as the Mediterranean diet.[18]

According to another 2014 review, intermittent fasting can lead to weight loss, though long-term calorie restriction can lead to slightly more weight loss compared to intermittent fasting.[19] Intermittent fasting has been found in healthy and obese adults to reduce basal insulin, triglycerides, and blood glucose in fasting periods shorter than 24 hours.[20] A 2014 review showed that intermittent fasting may reduce inflammation mechanisms and possibly affect cancer risk.[21] Reductions in weight, improvements in cardiovascular and metabolic variables, such as fat mass, LDL cholesterol, triglycerides, and C-reactive protein in non-obese individuals have been recorded.[22] Laboratory and preliminary human research indicates that intermittent fasting may influence metabolism of different food sources.[3][20]